1. Field of the Invention
The present invention pertains to a spray gun, such as is used for adhesive or similar materials, wherein a short burst of aerosol product is used to clean the spray gun tip before and after each application. The valve for the adhesive or similar material and the valve for the aerosol cleaner are both activated in sequence by the operation of a single trigger-like device. Additionally, the present invention uses xe2x80x9cbag-in-a-canxe2x80x9d technology, particularly for packages in excess of one liter, wherein a collapsible container holds the adhesive or similar material and is placed with a relatively rigid container designed to withstand the pressurization of the propellant charged between the collapsible container and the relatively rigid container.
2. Description of the Prior Art
In the prior art, aerosol products utilize a solvent to create a solvent or suspension that includes the liquified propellant. The early precursors of aerosols were xe2x80x9cbombsxe2x80x9d of the late nineteenth century which dissolved insecticides in hydrocarbon mixtures.
As technology and environmental concerns have progressed, water has become a required ingredient in aerosol products. However, water does not mix easily with propellant agents. Furthermore, film producing agents such as adhesives are designed with close tolerances with respect to miscibility and resistance to shear.
Most adhesives are comprised of synthetic polymers. However, in water-based adhesives, these polymers are simply suspended using surfactants. These surfactants are very specific in their functions within the system and are susceptible to swings in temperature, shear, pH or chemical contamination.
Additionally, adhesives are designed to create a film which is tacky and resistant to contaminants that may degrade the tacky characteristic. To create an industrial adhesive designed to bond two substrates under varying conditions of exposure to heat, water and solvents, the film must not soften and release its hold on the substrate. Therefore, the surfaces of application equipment, such as a spray gun, exposed to film curing must remain free of adhesive build-up. The prior art has not addressed how to avoid such adhesive build-up using a self-cleaning operation which does not require specific actions by the user which are separate and distinct from the adhesive application process.
Moreover, to a limited extent, the use of water-based products in aerosol packages (that is, self-contained, pre-pressurized containers) is known in the prior art for products. Formulations are also known, to a limited extent, which require complete segregation from the propellants (such as xe2x80x9cbag-in-a-canxe2x80x9d). However, this technology has apparently not been used successfully for an adhesive or in a package larger than one liter.
It is therefore an object of the present invention to provide an adhesive spray gun which remains free of adhesive build-up.
It is therefore a further object of the present invention to provide a cleaning operation for an adhesive or similar spray gun wherein the cleaning of the device is integrated into the operation of the device.
It is therefore a still further object of the present invention to provide an adhesive spray gun with simple and intuitive controls.
It is therefore a still further object of the present invention to utilize xe2x80x9cbag-in-a-canxe2x80x9d technology wherein the adhesive or similar product is placed within a collapsible bag which is placed within a relatively rigid container and wherein propellant is charged between the relatively rigid container and the collapsible bag.
It is therefore a still further object of the present invention to utilize the above technology for containers larger than one liter.
These and other objects are attained by using an application gun which is a modified airless applicator which includes a first port for receiving the adhesive or other primary product and a second port for receiving aerosol-based solvent cleaner. The adhesive or other primary product is supplied from a collapsible bag which is placed in a relatively rigid container with propellant charged between the bag and the relatively rigid container. A perforated dip tube is molded to the bag to act as a siphon for the adhesive or other primary product. The aerosol-based solvent cleaner is provided within a small aerosol container attached via a threaded valve stem in the handle of the gun.
The trigger assembly is designed to open and close the valves to the first and second ports in sequence whereby the first stage, typically as the trigger assembly is partially depressed, meters a volume of solvent cleaner via the second port directly to the tip. During the second stage, the first port is opened and the adhesive or other primary product is dispensed through the tip for as long as the trigger assembly is held fully depressed. When the trigger assembly is released at the end of the application, the trigger assembly momentarily passes again through the first stage and a second volume of solvent cleaner is metered or xe2x80x9cpoofedxe2x80x9d via the second port to the tip.
The apparatus is designed to work virtually simultaneously with the application process and is user-friendly with a reduced need for specific and separate maintenance operations. The apparatus further allows for a portable, self-contained supply of product and an automatic tip cleaning function. The apparatus is scalable, subject to weight and similar concerns. Furthermore, a wide range of products can be dispensed without the addition of ingredients that are hazardous to the user or to the environment.